WO2009121371A1

WO2009121371A1 - A fluid treatment unit comprising an ultrasound source

Info

Publication number: WO2009121371A1
Application number: PCT/DK2009/050074
Authority: WO
Inventors: Finn Beldring; Christian Rasmussen
Original assignee: Grundfos Management A/S
Priority date: 2008-04-02
Filing date: 2009-04-02
Publication date: 2009-10-08

Abstract

The present invention relates to a unit and a method for exposing fluid, typically being a liquid, to treatment. The invention relates in particular to a fluid treatment unit with a flow passage through which fluid may flow while being exposed to radiation emitted from an ultrasound source. The fluid treatment unit further comprises one or more total pressure increasing means for increasing the total pressure of fluid at least locally in the fluid treatment unit and a casing which encapsulates the flow passage and the one or more total pressure increasing means.

Description

A fluid treatment unit comprising an ultrasound source

Background of the invention

When fluid containing particles is subjected to pressure waves, in particular when resonance occurs, the particles can be exposed to very large accelerations. This may result in shear stresses and compressive stresses large enough to tear e.g. cell membranes apart or make particles break into smaller particles so that e.g. bacteria may be subjected to treatment with UV radiation and/or whereby e.g. bacteria are destroyed. Ultrasound treatment can also be used to mix and degrade long hydrocarbon chains.

Thus, fluids, and in particular water, are sometimes treated with ultrasound in order to destroy micro organisms such as bacteria or zooplankton. Such water treatment may be a preliminary, intermediate, or final step of a process involving other steps in which the treated water is used e.g. for rinsing of equipment. The fluid is typically exposed to ultrasound in a unit where the fluid flows past an ultrasound source, and this flow causes a pressure drop in the water treatment process. The pressure drop must be balanced by pressurisation means, such as a pump. Today this pressure drop is balanced by a pump arranged upstream or downstream of the treatment unit, as the combination of an ultrasound source and a pump is provided by stand-alone units connected with each other by piping. This piping often results in a complex construction being vulnerable to e.g. leakage. Furthermore, pipes and other connections often result in a pressure loss which must be overcome by the pump, and in system design the selection of the pump must take into account the pressure loss characteristics of the ultrasound device and the piping. This means that the engineer has to collect data and perform calculations. Disclosure of the invention

Thus, in a first aspect the present invention relates to a fluid treatment unit through which fluid may flow while being treated, the treatment comprising exposing the fluid to ultrasound and the fluid treatment unit comprising

a flow passage extending from an inlet to an outlet of the fluid treatment unit, one or more total pressure increasing means for at least partially overcoming the pressure loss due to the fluid flowing through the fluid treatment unit, the total pressure increasing means forming part of the flow passage, one or more ultrasound source(s) for emitting ultrasound into the at least a part of the flow passage and a casing encapsulating the flow passage and the total pressure increasing means,

wherein the ultrasound source(s) is/are arranged so that it/they is/are adapted to emit ultrasound into at least a part of the flow passage from a position inside the casing.

Thus, by use of fluid treatment units according to the present invention, the fluid leaving the treatment unit via the outlets has been exposed to ultrasound treatment, and inside the fluid treatment unit the total pressure of fluid being treated is increased at least locally by total pressure increasing means. In accordance with the present invention, a fluid treatment unit has a casing which preferably may be considered as a container-like structure inside which the one or more ultrasound sources and one or more total pressure increasing means are arranged. Thereby the need for connecting stand-alone units by pipes to provide a fluid treatment device may be avoided, and a compact unit meeting a given demand for treatment may be provided.

The fluid treatment will typically result in a pressure loss e.g. due to a flow path including bends and the like, and the total pressure increasing means is/are preferably used to overcome at least the pressure loss resulting from the fluid flowing through the fluid treatment unit.

Thus, while the known fluid treatment units are assembled by connecting a number of stand-alone units via pipes, the present invention is designed so that it preferably comprises a pressure carrying casing inside which the ultrasound source(s) and total pressure increasing means are arranged, whereby the unit may be made more compact and efficient. It should be mentioned that the ultrasound source may comprise one or more connections, e.g. electrical, one or more handles or the like extending outside the unit. The ultrasound generator may also be arranged outside the treatment unit. However, the interaction between the ultrasound source and the fluid preferably takes place inside the unit.

In the present context a number of terms are used. Although these terms are used in a manner ordinary to a person skilled in the art, a brief explanation of some of these terms will be presented below.

Ultrasound is preferably used to designate sound waves having a frequency above 20.000 Hz.

Source channel is preferably used to designate a part of the flow path in which the ultrasound emitting part of the ultrasound source is placed.

Casing is preferably used to designate the wall of the fluid treatment unit. This wall confines fluid in the fluid treatment unit so that fluid may flow into and out of the treatment unit through one or more inlets and outlets provided in the casing. The casing may comprise a number of wall elements.

Velocity inducer is preferably used to designate an element inducing velocity to the fluid so that its direction and/or total pressure is changed. In some embodiments such a velocity inducer is an impeller.

Total pressure is preferably used to designate the sum of the static and the dynamic pressure in the fluid. Fluid is preferably used to designate at least liquid, gas, a fluidized medium or combinations thereof.

Inlet/outlet is preferably used to designate a cross section or a region where fluid flows into or out of an element. The inlet/outlet may preferably be an end cross section or a region of a pipe, channel or the like. Inlet and outlet may preferably also be considered as the sections of a control volume through which fluid flows into or out of the element, this control volume encircling the element in question.

The total pressure increasing means may comprise one or more velocity inducers, and at least one of the total pressure increasing means may comprise one or more impellers. The one or more impellers may be arranged on a shaft connected to a motor.

Some embodiments of the invention comprise two or more impellers of which some or all may be arranged on a common shaft.

The flow passage through the fluid treatment unit may further comprise one or more source channels each at least partly surrounding at least one ultrasound source. Such source channels establish a part of the flow passage, and it may have a shape and dimensions which ensure that fluid flowing through the source channel is led close to the ultrasound source. Hereby it may be obtained that the fluid is treated with ultrasound having as high intensity as possible.

In preferred embodiments of the invention, the ultrasound source(s) is/are elongated and has/have a length axis. However, any shape and type of ultrasound source is possible within the scope of the present invention.

A fluid treatment unit according to the present invention may comprise one or more treatment stages each comprising a flow passage forming part of the flow passage through the fluid treatment unit. Hereby a fluid treatment unit may have a modular configuration which can easily be designed for a given application or adjusted to correspond to a modified treatment requirement. All of the flow passage(s) of one or more of the treatment stages may comprise two cavities being in fluid communication with each other via a source channel. Each treatment stage may comprise at least one total pressure increasing means, and each treatment stage may further comprise at least one ultrasound source.

In embodiments comprising at least one impeller, at least one ultrasound source may be arranged so that the ultrasound waves are generated to propagate radially with respect to an impeller. Alternatively at least one ultrasound source may be arranged so that the ultrasound waves are generated to propagate tangentially with respect to an impeller.

In any of the embodiments described above, the ultrasound may have a frequency of 20,000 to 30,000 Hz, such as 20,000 to 25,000 Hz or 25,000 to 30,000 Hz. However, any frequency above 20,000 Hz is possible within the scope of the present invention.

In embodiments comprising two or more ultrasound sources, each ultrasound source may be elongated, and the two ore more ultrasound sources may be oriented in one of two perpendicular directions so that there is at least one ultrasound source in each direction.

In alternative embodiments comprising two or more ultrasound sources, each ultrasound source may be elongated, and the two or more ultrasound sources may be arranged parallel to each other.

Any of the embodiments of the invention comprising two or more treatment stages each comprising a flow passage forming part of the flow passage through the fluid treatment unit, may comprise one ultrasound source in each stage.

In any of the embodiments comprising two or more ultrasound sources, the ultrasound sources may be adapted to emit ultrasound with substantially the same frequency. Alternatively, at least two of the ultrasound sources may be adapted to emit ultrasound with different frequencies. Different frequencies may e.g. be chosen to obtain different treatment processes. A fluid treatment unit according to the present invention may further comprise a throttle valve. Such a valve may typically be arranged so that it can be used to control the flow through the outlet. The purpose may e.g. be to ensure that a measured property of the fluid is kept constant, below a predefined threshold, or above a predefined threshold. The threshold may e.g. a maximum acceptable concentration of a specific type of impurities in the fluid. If the property does no have a desired value, it may be necessary to let at least some of the fluid flow through the fluid treatment unit again. More than one property may also be determined and compared to a threshold value.

A fluid treatment unit as described above may therefore further comprise means for recirculating fluid that has flown through at least a part of the flow passage to flow through at least a part of the flow passage again. Such recirculation may be performed inside the casing, or it may be performed by transporting fluid from the outlet to the inlet of the fluid treatment unit. When the recirculation is performed inside the casing, it may comprise that the fluid is recirculated inside a stage, e.g. dependent on a controllable rotational speed of an impeller, or that is led from an outlet of a stage and back to the inlet of that stage. Recirculation may e.g. be relevant if measurements indicate that the fluid has not been sufficiently treated by a first flow through at least a part of the flow passage, Such measurements may be made by use of sensors placed e.g. inside a source channel or at the outlet of the fluid treatment unit.

A fluid treatment unit according to the present invention may further comprise one or more light source(s) and have one or more sections of surfaces of the flow passage being exposed to light emitted from the one or more light source(s) which surfaces is/are coated with or being made from a photo catalytic substance.

In some embodiments such a light source may be an ultraviolet lamp. The photo catalytic substance may be TiO₂.

The purpose of such coating may be to obtain a photo catalytic conversion of e.g.

H₂O into OH^", This has shown to have advantageous effect in cleaning e.g. water.

Furthermore, there may, at least for some treatment applications, be a synergistic effect between the ultrasound treatment and the photo catalytic treatment. Alternatively or in combination therewith, TiO₂ particles can be added to the fluid, e.g. before the fluid is led into the fluid processing unit.

In a second aspect the present invention relates to a method of treating fluid, the method comprising letting fluid flow through a fluid treatment as described above. Such a method may further comprise that photo catalytic particles, such as TiO₂ particles, are present in the fluid.

In a third aspect the present invention relates to a method of controlling a fluid treatment unit as described above, wherein a throttle valve is used to control the flow of fluid out of the unit so that a measured property of the fluid is kept constant, below a predefined threshold, or above a predefined threshold. The threshold may e.g. a maximum acceptable concentration of a specific type of impurities in the fluid.

In a method of controlling a fluid treatment unit as described above wherein the fluid treatment unit comprises one or more impellers, the method may comprise controlling the rotational speed of the one or more impeller(s) so that a predetermined flow rate is obtained or maintained.

Further embodiments of the present invention are presented below and in the claims. The present invention and in particular preferred embodiments thereof will now be disclosed in connection with the accompanying drawings in which:

Fig. 1 is a schematic three-dimensional view of an embodiment of a fluid treatment unit according to the present invention.

Fig. 2 shows schematically a treatment stage of a fluid treatment unit according to an embodiment of the invention. Fig. 2a shows the treatment stage in a partly exploded view and fig. 2b shows a segment of a cross sectional view taken along line A-A in fig. 2a.

Fig. 3 shows schematically a cross sectional view along a diameter of a cylindrical treatment section having three treatment stages. Fig. 4 shows a cross sectional view of a source channel in which an ultrasound horn and a flow guide are inserted.

Fig. 5 shows schematically that for some embodiments having at least one impeller, the ultrasound source may be arranged so that the ultrasound waves are generated to propagate radially or tangentially, respectively, with respect to an impeller.

Fig. 6 shows schematically a longitudinal cross section of a fluid treatment unit according to the present invention. The unit comprises seven stages, an inlet element, an outlet element, and a motor for rotating impellers arranged in the fluid treatment unit. Fig. 6 shows in particular an embodiment of assembling the fluid treatment unit shown.

Fig. 7 shows schematically a cross sectional view of an end-suction pump comprising an ultrasound source.

Detailed description of preferred embodiments of the present invention

Fig. 1 shows schematically a three dimensional view of a first embodiment of a fluid treatment unit according to present invention. With reference to fig. 1, the treatment unit 1 comprises a treatment section 2 with sealable connections 3a and 3b for receiving an ultrasound source and elements cooperating with the ultrasound source - this will be explained in greater details below.

On the top and on the bottom of the treatment section 2, an outlet element 4 and inlet element 5 are arranged, respectively. The inlet element 5 comprises an inlet 6 through which the fluid to be processed enters into the unit 1, and the outlet element 4 comprises an outlet 7 through which processed fluid leaves the unit 1. The inlet element 5 and the outlet element 4 are sealed to the treatment stage 2 to prevent fluid from leaking out from the unit.

An electric motor 8 is arranged on the outlet element 4 by a motor fixture 9, and the shaft 10 of the motor 8 extends through the outlet element 4 and into the interior of the treatment unit 1. The penetration of the shaft 10 through the wall of the outlet element 4 is sealed to avoid fluid from leaking out of the treatment unit 1 along the shaft 10.

Thus, the treatment unit 1 constitutes, when assembled, a sealed unit where fluid enters into the unit through the inlet 6 and leaves the unit through outlet 7.

The ultrasound emission results in micro cavitations where the local pressure in the fluid is so low that the boiling point is below the boiling point of the surroundings. Small steam bubbles are formed, and when they collapse/implode, a large pressure pulse is formed which may damage e.g. bacteria (when present in the fluid) if the cell membranes are damaged. The micro cavitations are formed where the material cannot follow the pulses; i.e. not necessarily at a solid surface, such as the surface of the ultrasound horn.

Fig. 2. a and 2.b show a particular embodiment of a treatment section 2. The treatment section 2 is shown in a partly exploded view (fig. 2. a) and comprises an ultrasound horn 11. When in use, the ultrasound horn 11 and the flow guide 13 are inserted in the socket 21. Fig. 2.b shows a segment of a cross sectional view taken along line A-A in figure 2. a, i.e. perpendicular to the ultrasound horn and along a radius of the treatment section 2 with the shaft 10 removed. Arrows labeled F in fig. 2.b indicate the flow of the fluid through the treatment section 2. Please note that in fig. 2 the fluid flows downwards (with respect to the orientation of the figure), whereas in fig. 1 it flows upwards.

As shown in fig 2. a and 2.b, the treatment unit comprises a cylindrical casing part 14 and a floor element 15 dividing the treatment section 2 into two cavities, a first cavity 16 located above the floor element 15 and a second cavity 17 located below the floor element 15. The two cavities 16,17 are in fluid communication with each other through a source channel 18.

The ultrasound generator 12 comprises an ultrasound horn 11 which is arranged to emit ultrasound to the source channel 18. A flow guide 13 is also arranged within the source channel 18. The flow guide 13 leaves a passage open between the ultrasound horn 11 and the end of the flow guide 13 whereby the flow guide 13 assist in guiding the fluid towards the ultrasound horn 11. The flow guide 13 may furthermore be excited by the sound waves emitted from the ultrasound horn 11 and thereby constitute a surface at which the ultrasound waves are transferred to the fluid. The flow guide 13 may have a design resulting in resonance due to eigenfrequencies; this can be used to focus the wave propagation and thereby make the treatment of the fluid more effective.

An impeller 19 is arranged in the treatment section 2 as shown in fig. 2b (the impeller 19 has been left out in fig. 2a for clarity reasons only). The rotation of the impeller 19 is effectuated by the rotation of the shaft 10 on which the impeller 19 is arranged. The impeller 19 receives fluid from the inlet 6 (not shown in fig. 2.b) and due to the rotation of the impeller 19, the momentum of the fluid is increased during its passage of the impeller 19 where after the fluid leaves the impeller 19 in radial direction of the treatment section 2 and flows into the cavity 16.

The treatment section in fig. 1 and 2 is shown to comprise one treatment stage, where a stage is considered as a unit having two cavities 16,17 separated by a floor element 15. However, a treatment section may comprise a number of such treatment stages, which may be stacked, to enhance treatment of the fluid flowing through the treatment unit 1. The treatment stages may in such configurations be configured equally with respect to ultrasound sources, or the treatment stages may be configured differently; e.g. the frequency and/or energy emitted may be varied between the various stages.

It may furthermore be possible to combine ultrasound treatment stages with corresponding stages performing other types of treatment such as treatment with ultraviolet light, heating, addition of further substances etc..

Fig. 3 is a cross sectional view of a fluid treatment unit having three treatment stages. Fluid to be treated flows via an inlet 6 to the impeller 19c in which the pressure of the fluid is increased. The fluid flows out of the impeller 19c in a spiraling motion towards and into source channel 18c. The fluid flows out through the outlet 20a and into the outlet element 4 (see fig. 1). In Fig. 3 the three treatment stages 2a, 2b, 2c are similar to each other. However, the actual number of stages may be varied, and the stages may not always be similar to each other, a, b and c in the following refer to these three stages.

Each treatment stage 2, comprises a fluid velocity inducer 19, a stage connecting passage 20, and a source channel 18. In the embodiment shown in fig. 3, the fluid velocity inducers 19 are in the form of rotating impellers receiving fluid in an axial direction through a stage connecting passage 20 (or through the inlet for stage c) and delivering fluid at a higher velocity in radial direction as indicated by arrows in fig. 3. In the embodiment of fig. 3, the extension of the source channel 18 is perpendicular to the plane of the paper.

The ultrasound vibrations are transferred to and via the solid parts of the treatment unit, and the fluid is therefore exposed to ultrasound also outside the source channels. The actual effect of the ultrasound is related not only to the frequency but also to the intensity of the ultrasound waves. An impeller shaft 10 is provided for rotating all impellers 19 in common, and the impeller shaft 10 is connected to a motor 8 (see fig. 1). Thus, when activating the motor 8, the impellers 19 are rotating whereby fluid is drawn into the treatment section 2 through the inlet 6.

Fig. 4 shows a cross sectional view through the source channel 18. All the fluid passing through the treatment section 2 is passing through the source channel 18, and the dimensioning of the source channel 18 is so that the fluid flows in close vicinity of the ultrasound source. Hereby it is ensured that the fluid is treated by ultrasound waves having as high intensity as possible. The distance D between the ultrasound horn 11 and the fluid guide 13 may be variable so that resonance can be obtained. Hereby the effect of the ultrasound waves can be made as efficient as possible.

It should be mentioned that although the treatment stages 2 shown in fig.s 2-4 are shown to comprise only one source channel 18, more than one source channel 18 may be provided in a stage 2. Furthermore, the mutual orientation of the source channels 18 in one or more stage(s) may be varied, e.g. two or more source channels 18 may be orientated similar to each other or different to each other.

When a stage 2 comprises more than one ultrasound horn 11, these may be arranged either in parallel or in serial arrangement; i.e. that only some of the fluid passes each ultrasound horn 11 or that all fluid passes all the ultrasound horns 11, respectively. Parallel arrangement is in particular useful for a high flow rate and a low demand for exposure, whereas a serial arrangement is in particular useful for a low flow rate and a high demand for exposure. A low flow rate may e.g. be defined to be in the order of 2 m3 per hour.

Figure 5 shows schematically two possible mutual orientations of an ultrasound horn 11 and an impeller 19. The waves are generated to flow radially and tangentially, respectively, with respect to the impeller. Other orientations are also possible within the scope of the invention.

In some embodiments, the ultrasound source 11 of a stage 2 is an integral part of the stage 2 in the sense that it is non-removable, and in other embodiments the stages 2 are provided with a socket 21 that enables removal of the ultrasound source 11.

A pressure increasing step may be provided in the outlet element 4 or the inlet element 5 by arranging a number of impellers to form a pressure increasing stack of impellers which impellers are arranged on the common shaft 10. Alternatively the impellers in the pressure increasing step may be arranged on another shaft driven by another motor. The pressure increase provided by the stack of impellers may be larger than the pressure drop resulting from the flow and treatment of the fluid in the stages 2, and the fluid thereby leaves the fluid treatment unit 1 at an increased pressure level relatively to the pressure of the fluid at the inlet 6.

Fig. 6 shows schematically a longitudinal cross section of a fluid treatment unit 1 according to the present invention, and shows in particular one way of assembling the unit. The unit is formed as an elongated unit having a cylindrical casing 14 and comprises seven stages 2, an inlet element 5, an outlet element 4 and a motor 8 arranged on a fixture 9 with a shaft 10 for rotating impellers (not shown) arranged in the fluid treatment unit 1. Radiation sources as well as the flow passages are not shown in the figure. The stages 2 may be in the form shown in the previous figures with corresponding descriptions. The inlet element 5 and the outlet element 4 are considered as part of the casing.

In the embodiment illustrated in fig. 6, the stages 2 and elements 4,5 are assembled by a fluid treatment unit assembling fixture 21 comprising a number of stay bolts 22 extending along the longitudinal direction of fluid treatment unit 1 and penetrating clamps 23. Nuts 24 are provided on the ends of the stay bolts 22 so that when the nuts 24 are tightened, the clamps 23 will provide a longitudinal force to the fluid treatment unit 1 so that the elements 4,5 and stages 2 are held together in the longitudinal direction. The shaft 10 extends from the motor 8 to a bearing 31 arranged in the inlet element 5.

Securing of the elements 4,5 and stages 2 in a direction perpendicular to the longitudinal direction of the fluid treatment unit 1 is shown as being provided by ring shaped guides 25 into which the elements 4,5 and stages 2 fit snugly. Sealing of the fluid treatment unit is provided by applying o-rings (not shown) e.g. in grooves (not shown) provided in the ring shaped guides 25. Alternatively, or in combination thereto, the ring shaped guides 25 may be formed as assembling rings 26 arranged inside the fluid treatment unit as shown in fig. 2. The shaft 10 extends from the motor 8 to a bearing ?? arranged in the inlet element 5.

In some situations recirculation of fluid may be advantageous, e.g. if fluid having flown through one or more source channels 18 has not been sufficiently exposed to the ultrasound treatment. In fluid treatment units according to the present invention, fluid may therefore be re-circulated to flow through part of or the whole treatment unit again. The recirculation may e.g. be performed internally in the unit by e.g. arranging a closeable connection in the floor element 15 of the embodiment shown in fig. 3 and/or fluid may be re-directed from the outlet 7 to the inlet 6 by a suitable valve system.

In some embodiments a throttle valve is placed at the outlet whereby the flow rate out of the fluid treatment unit can be regulated. This can be used to increase the treatment time possibly in combination with a regulation of the rotational speed of one or more impellers.

Although the description of the present invention presented herein focuses on impellers for driving the fluid through the fluid treatment unit 1, other types of pressurisation means may be used. However, in connection with the present invention it has been found that impellers 19 are advantageous, as the impellers provide a flow which includes a swirling velocity component in the fluid flowing through the one or more of the stages 2 or the whole fluid treatment unit 1. Such a swirling velocity component may be used to increase the interaction with the ultrasound source 11 in the fluid treatment unit 1 which may be utilised to process the fluid more intensively while keeping the overall outer dimensions of the fluid treatment unit 1 low and the velocity in the unit high. This is due to the fact that the swirling velocity component can be used to obtain that the fluid passes the ultrasound source more than once, before it leaves the stage.

In many practical implementations it has been found valuable to measure the intensity or energy of the ultrasound emitted into the fluid flowing through the source channel 18, typically as a step in establishing whether the fluid has been exposed to ultrasound sufficient to e.g. destroy bacteria or the like or whether a higher degree of recirculation is necessary. In preferred embodiments, a sensor (not shown) is arranged in the wall of the source channel 18. Alternatively or in combination therewith, one or more properties of the fluid may be measured at the outlet and used to ensure that one or more parameters is/are kept constant, below a predefined threshold, or above a predefined threshold. The threshold may e.g. a maximum acceptable concentration of a specific type of impurities in the fluid. If the property does no have a desired value, it may be necessary to let at least some of the fluid flow through the fluid treatment unit again.

Utilisation of fluid treatment units comprising a number of stackable stages is very convenient where treatment units need to be tailored to a specific need - for instance various treatment technologies may be combined by combining cassettes with the various treatment technologies, and a given treatment capacity may be matched by stacking a number of stages. Fig. 7 shows schematically an alternative embodiment of the invention where an ultrasound source 11 is placed inside the casing 14 of an end-suction pump 26. The fluid is pumped through the pump 26 by an impeller 19 mounted on a shaft 10 driven by a motor 8. The fluid enters the pump 26 via the inlet 6, and leaves the pump 26 via the outlet 7 which is typically connected to a pipe 27. The ultrasound source 11 is placed inside the pump 26 in such a way that the fluid flows along the ultrasound source 11 and is thereby subjected to the ultrasound exited there from. The ultrasound generator 12 and the counterweight 28 of the ultrasound generator are placed inside a counterweight housing 29 mounted on the casing 14 of the pump 26. In an alternative embodiment (not shown), the ultrasound source 11 is placed so that the fluid is subjected to ultrasound before passing the impeller 19.

In addition to the embodiments described above, ultrasound may be used to improve the efficiency of other fluid treatment processes. Examples include the following combinations:

with mixing of two or more fluids, such as addition of chemicals to a fluid, or mixing with solid, such as particulates, - enzyme processes to accelerate the processes, for decomposition of particles or agglomerates of particles added to the fluid as part of the treatment or particles to be removed from the fluid.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

1. A fluid treatment unit through which fluid may flow while being treated, the treatment comprising exposing the fluid to ultrasound and the fluid treatment unit comprising - a flow passage extending from an inlet to an outlet of the fluid treatment unit, one or more total pressure increasing means for at least partially overcoming the pressure loss due to the fluid flowing through the fluid treatment unit, the total pressure increasing means forming part of the flow passage, one or more ultrasound source(s) for emitting ultrasound into the at least a part of the flow passage, and a casing encapsulating the flow passage and the total pressure increasing means, wherein the ultrasound source(s) is/are arranged so that it/they is/are adapted to emit ultrasound into at least a part of the flow passage from a position inside the casing.

2. A fluid treatment unit according to claim 1, wherein the total pressure increasing means comprise(s) one or more velocity inducers.

3. A fluid treatment unit according to claim 2, wherein at least one of the total pressure increasing means comprise(s) one or more impellers.

4. A fluid treatment unit according to claim 3, wherein the one or more impellers is/are arranged on a shaft connected to a motor.

5. A fluid treatment unit according to claim 3 or 4, comprising two or more impellers of which some or all are arranged on a common shaft.

6. A fluid treatment unit according to any of the preceding claims, wherein the flow passage through the fluid treatment unit further comprises one or more source channels each at least partly surrounding at least one ultrasound source.

7. A fluid treatment unit according to any of the preceding claims, wherein the ultrasound source(s) is/are elongated and has/have a length axis.

8. A fluid treatment unit according to any of the preceding claims, wherein the fluid treatment unit comprises one or more treatment stages each comprising a flow passage forming part of the flow passage through the fluid treatment unit.

9. A fluid treatment unit according to claim 8, wherein some or all of the flow passage(s) of one or more of the treatment stages comprise(s) two cavities being in fluid communication with each other via a source channel.

10. A fluid treatment unit according to claim 8 or 9, wherein each treatment stage comprises at least one total pressure increasing means.

11. A fluid treatment unit according to any of claims 8-10, wherein each treatment stage comprises at least one ultrasound source.

12. A. fluid treatment unit according to claim 3 or any of claims 4 to 11 when dependent on claim 3, wherein at least one ultrasound source is arranged so that the ultrasound waves are generated to propagate radially with respect to an impeller.

13. A. fluid treatment unit according to claim 3 or any of claims 4 to 11 when dependent on claim 3, wherein at least one ultrasound source is arranged so that the ultrasound waves are generated to propagate tangentially with respect to an impeller.

14. A fluid treatment unit according to any of the preceding claims, wherein the ultrasound has a frequency of 20,000 to 30,000 Hz, such as 20,000 to 25,000 Hz or 25,000 to 30,000 Hz.

15. A fluid treatment unit according to any of the preceding claims, comprising two or more ultrasound sources each being elongated and being arranged in one of two perpendicular directions so that there is at least one ultrasound source in each direction.

16. A fluid treatment unit according to any of claims 1 to 14, comprising two or more ultrasound sources each being elongated and being arranged parallel to each other.

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17. A fluid treatment unit according to claim 15 or 16 when dependent on claim 8, comprising two or more stages with one ultrasound source in each stage.

18. A fluid treatment unit according to any of the preceding claims, comprising 10 two or more ultrasound sources adapted to emit ultrasound with substantially the same frequency.

19. A fluid treatment unit according to any of the preceding claims, comprising two or more ultrasound sources of which at least two are adapted to emit

15 ultrasound with different frequencies.

20. A fluid treatment unit according to any of the preceding claims further comprising a throttle valve.

20 21. A fluid treatment unit according to any of the preceding claims, further comprising means for recirculating fluid that has flown through at least a part of the flow passage to flow through at least a part of the flow passage again.

22. A fluid treatment unit according to claim 21, wherein the recirculation is 25 performed inside the casing.

23. A fluid treatment unit according to claim 21, wherein the recirculation is performed by transporting fluid from the outlet to the inlet of the fluid treatment unit.

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24. A fluid treatment unit according to any of the preceding claims further comprising one or more light source(s) and wherein one or more sections of surfaces of the flow passage being exposed to light emitted from the one or more light source(s) is/are coated with or made from a photo catalytic substance.

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25. A fluid treatment unit according to claim 24, wherein the light source is an ultraviolet lamp.

26. A fluid treatment unit according to claim 24 or 25, wherein at least some of 5 the photo catalytic substance is TiO₂.

27. A method of treating fluid, the method comprising letting fluid flow through a fluid treatment unit according to any of the preceding claims.

10 28. A method of treating fluid according to claim 27, wherein photo catalytic particles, such as TiO2 particles, are present in the fluid.

29. A method of controlling a fluid treatment unit according to any of claims 1 to 26, wherein a throttle valve is used to control the flow of fluid out of the unit so

15 that a measured property of the fluid is kept constant, below a predefined threshold, or above a predefined threshold.

30. A method of controlling a fluid treatment unit according to any of the preceding claims 3 or 4-26 when dependent on claim 3, the method comprising

20 controlling the rotational speed of the one or more impeller(s) so that a predetermined flow rate is obtained or maintained.